Treatment methods for nahcolitic oil shale formations with fractures

ABSTRACT

A method for treating a hydrocarbon containing layer in a subsurface formation includes forming a plurality of substantially vertical fractures in the formation at selected intervals along a length of at least one production wellbore positioned substantially horizontally in the hydrocarbon containing layer. Heat is provided from a plurality of heaters to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized. At least some of the plurality of heaters are positioned substantially horizontally in the hydrocarbon containing layer. At least some mobilized hydrocarbons are produced through at least one production wellbore.

This application claims the benefit of U.S. Provisional Application No. 61/620,526, filed Apr. 5, 2012, which is incorporated herein by reference.

RELATED PATENTS

This patent application incorporates by reference in its entirety each of U.S. Pat. Nos. 6,688,387 to Wellington et al.; 6,991,036 to Sumnu-Dindoruk et al.; 6,698,515 to Karanikas et al.; 6,880,633 to Wellington et al.; 6,782,947 to de Rouffignac et al.; 6,991,045 to Vinegar et al.; 7,073,578 to Vinegar et al.; 7,121,342 to Vinegar et al.; 7,320,364 to Fairbanks; 7,527,094 to McKinzie et al.; 7,584,789 to Mo et al.; 7,533,719 to Hinson et al.; 7,562,707 to Miller; and 7,798,220 to Vinegar et al.; U.S. Patent Application Publication Nos. 2009-0189617 to Burns et al.; 2010-0071903 to Prince-Wright et al.; 2010-0096137 to Nguyen et al.; and 2010-0258265 to Karanikas et al.

BACKGROUND

1. Field of the Invention

The present invention relates generally to methods and systems for production of hydrocarbons, hydrogen, and/or other products from various subsurface formations such as hydrocarbon containing formations.

2. Description of Related Art

In situ processes may be used to treat subsurface formations. During some in situ processes, fluids may be introduced or generated in the formation. Introduced or generated fluids may need to be contained in a treatment area to minimize or eliminate impact of the in situ process on adjacent areas. During some in situ processes, a barrier may be formed around all or a portion of the treatment area to inhibit migration of fluids out of or into the treatment area.

A low temperature zone may be used to isolate selected areas of subsurface formation for many purposes. U.S. Pat. Nos. 7,032,660 to Vinegar et al.; 7,435,037 to McKinzie, II; 7,527,094 to McKinzie et al.; 7,500,528 to McKinzie, II et al.; and 7,631,689 to Vinegar et al., and U.S. Patent Application Publication No. 20080217003 to Kulhman et al. and 20080185147 to Vinegar et al., each of which is incorporated by reference as if fully set forth herein, describe barrier systems for subsurface treatment areas.

In some systems, ground is frozen to inhibit migration of fluids from a treatment area during soil remediation. U.S. Pat. Nos. 4,860,544 to Krieg et al.; 4,974,425 to Krieg et al.; 5,507,149 to Dash et al., 6,796,139 to Briley et al.; and 6,854,929 to Vinegar et al., each of which is incorporated by reference as if fully set forth herein, describe systems for freezing ground.

As discussed above, there has been a significant amount of effort to develop methods and systems to economically produce hydrocarbons, hydrogen, and/or other products from hydrocarbon containing formations. At present, however, there are still many hydrocarbon containing formations from which hydrocarbons, hydrogen, and/or other products cannot be economically produced. Thus, there is a need for improved methods and systems for heating of a hydrocarbon formation and production of fluids from the hydrocarbon formation. There is also a need for improved methods and systems that contain water and production fluids within a hydrocarbon treatment area.

SUMMARY

Embodiments described herein generally relate to systems and methods for treating a subsurface formation. In certain embodiments, the invention provides one or more systems and/or methods for treating a subsurface formation.

In certain embodiments, a method for treating a hydrocarbon containing layer in a subsurface formation includes: forming a plurality of substantially vertical fractures in the formation at selected intervals along a length of at least one production wellbore positioned substantially horizontally in the hydrocarbon containing layer; providing heat from a plurality of heaters to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized, wherein at least some of the plurality of heaters are positioned substantially horizontally in the hydrocarbon containing layer; and producing at least some mobilized hydrocarbons through at least one production wellbore.

In certain embodiments, a method for treating a hydrocarbon containing layer in a subsurface formation includes: forming a plurality of substantially vertical fractures in the formation at selected intervals along lengths of a plurality of production wellbores positioned substantially horizontally in the hydrocarbon containing layer; providing heat from a plurality of heaters to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized, wherein at least some of the plurality of heaters are positioned substantially horizontally in the hydrocarbon containing layer; and producing at least some mobilized hydrocarbons through at least one of the production wellbores.

In some embodiments, a system configured for treating a hydrocarbon containing layer in a subsurface formation includes: a plurality of production wellbores positioned substantially horizontally in the hydrocarbon containing layer; a plurality of heaters positioned substantially horizontally in the hydrocarbon containing layer, wherein the heaters are configured to provide heat to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized during use; and a plurality of substantially vertical fractures formed in the formation at selected intervals along a length of at least one of the production wellbores.

In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments.

In further embodiments, treating a subsurface formation is performed using any of the methods, systems, power supplies, or heaters described herein.

In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

FIG. 1 shows a schematic view of an embodiment of a portion of an in situ heat treatment system for treating a hydrocarbon containing formation.

FIG. 2 depicts an embodiment of a solution mining well.

FIG. 3 depicts an elevational view of a well pattern for solution mining and/or an in situ heat treatment process.

FIG. 4 depicts a representation of wells of an in situ heating treatment process for solution mining and producing hydrocarbons from a formation.

FIG. 5 depicts a cross-sectional representation of an embodiment of a treatment area being partially solution mined using selected layers of hydrocarbon containing layer.

FIG. 6 depicts a representation of an embodiment of a portion of a treatment area that is orthogonal to the treatment area depicted in FIG. 5.

FIGS. 7A-C depict an embodiment for treating a formation using an in situ heat treatment process with vertical production wells.

FIGS. 8A-C depict an embodiment for treating a formation using an in situ heat treatment process with horizontal production wells and fractures initiated in the production wells.

FIGS. 9A-B depict another embodiment for treating a formation using an in situ heat treatment process with horizontal production wells and fractures initiated in the production wells

FIGS. 10A-B depict an embodiment for treating a formation with fluid injection through fractures initiated in production wells.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

The following description generally relates to systems and methods for treating hydrocarbons in the formations. Such formations may be treated to yield hydrocarbon products, hydrogen, and other products.

“API gravity” refers to API gravity at 15.5° C. (60° F.). API gravity is as determined by ASTM Method D6822 or ASTM Method D1298.

“Asphalt/bitumen” refers to a semi-solid, viscous material soluble in carbon disulfide. Asphalt/bitumen may be obtained from refining operations or produced from subsurface formations.

“Carbon number” refers to the number of carbon atoms in a molecule. A hydrocarbon fluid may include various hydrocarbons with different carbon numbers. The hydrocarbon fluid may be described by a carbon number distribution. Carbon numbers and/or carbon number distributions may be determined by true boiling point distribution and/or gas-liquid chromatography.

“Condensable hydrocarbons” are hydrocarbons that condense at 25° C. and one atmosphere absolute pressure. Condensable hydrocarbons may include a mixture of hydrocarbons having carbon numbers greater than 4. “Non-condensable hydrocarbons” are hydrocarbons that do not condense at 25° C. and one atmosphere absolute pressure. Non-condensable hydrocarbons may include hydrocarbons having carbon numbers less than 5.

“Coupled” means either a direct connection or an indirect connection (for example, one or more intervening connections) between one or more objects or components. The phrase “directly connected” means a direct connection between objects or components such that the objects or components are connected directly to each other so that the objects or components operate in a “point of use” manner.

“Cracking” refers to a process involving decomposition and molecular recombination of organic compounds to produce a greater number of molecules than were initially present. In cracking, a series of reactions take place accompanied by a transfer of hydrogen atoms between molecules. For example, naphtha may undergo a thermal cracking reaction to form ethene and H₂.

A “fluid” may be, but is not limited to, a gas, a liquid, an emulsion, a slurry, and/or a stream of solid particles that has flow characteristics similar to liquid flow.

“Fluid injectivity” is the flow rate of fluids injected per unit of pressure differential between a first location and a second location.

“Fluid pressure” is a pressure generated by a fluid in a formation. “Lithostatic pressure” (sometimes referred to as “lithostatic stress”) is a pressure in a formation equal to a weight per unit area of an overlying rock mass. “Hydrostatic pressure” is a pressure in a formation exerted by a column of water.

A “formation” includes one or more hydrocarbon containing layers, one or more non-hydrocarbon layers, an overburden, and/or an underburden. “Hydrocarbon layers” refer to layers in the formation that contain hydrocarbons. The hydrocarbon layers may contain non-hydrocarbon material and hydrocarbon material. The “overburden” and/or the “underburden” include one or more different types of impermeable materials. For example, the overburden and/or underburden may include rock, shale, mudstone, or wet/tight carbonate. In some embodiments of in situ heat treatment processes, the overburden and/or the underburden may include a hydrocarbon containing layer or hydrocarbon containing layers that are relatively impermeable and are not subjected to temperatures during in situ heat treatment processing that result in significant characteristic changes of the hydrocarbon containing layers of the overburden and/or the underburden. For example, the underburden may contain shale or mudstone, but the underburden is not allowed to heat to pyrolysis temperatures during the in situ heat treatment process. In some cases, the overburden and/or the underburden may be somewhat permeable.

“Formation fluids” refer to fluids present in a formation and may include pyrolyzation fluid, synthesis gas, mobilized hydrocarbons, and water (steam). Formation fluids may include hydrocarbon fluids as well as non-hydrocarbon fluids. The term “mobilized fluid” refers to fluids in a hydrocarbon containing formation that are able to flow as a result of thermal treatment of the formation. “Produced fluids” refer to fluids removed from the formation.

A “heat source” is any system for providing heat to at least a portion of a formation substantially by conductive and/or radiative heat transfer. For example, a heat source may include electrically conducting materials and/or electric heaters such as an insulated conductor, an elongated member, and/or a conductor disposed in a conduit. A heat source may also include systems that generate heat by burning a fuel external to or in a formation. The systems may be surface burners, downhole gas burners, flameless distributed combustors, and natural distributed combustors. In some embodiments, heat provided to or generated in one or more heat sources is supplied by other sources of energy. The other sources of energy may directly heat a formation, or the energy may be applied to a transfer medium that directly or indirectly heats the formation. It is to be understood that one or more heat sources that are applying heat to a formation may use different sources of energy. Thus, for example, for a given formation some heat sources may supply heat from electrically conducting materials, electric resistance heaters, some heat sources may provide heat from combustion, and some heat sources may provide heat from one or more other energy sources (for example, chemical reactions, solar energy, wind energy, biomass, or other sources of renewable energy). A chemical reaction may include an exothermic reaction (for example, an oxidation reaction). A heat source may also include an electrically conducting material and/or a heater that provides heat to a zone proximate and/or surrounding a heating location such as a heater well.

A “heater” is any system or heat source for generating heat in a well or a near wellbore region. Heaters may be, but are not limited to, electric heaters, burners, combustors that react with material in or produced from a formation, and/or combinations thereof.

“Heavy hydrocarbons” are viscous hydrocarbon fluids. Heavy hydrocarbons may include highly viscous hydrocarbon fluids such as heavy oil, tar, and/or asphalt. Heavy hydrocarbons may include carbon and hydrogen, as well as smaller concentrations of sulfur, oxygen, and nitrogen. Additional elements may also be present in heavy hydrocarbons in trace amounts. Heavy hydrocarbons may be classified by API gravity. Heavy hydrocarbons generally have an API gravity below about 20°. Heavy oil, for example, generally has an API gravity of about 10-20°, whereas tar generally has an API gravity below about 10°. The viscosity of heavy hydrocarbons is generally greater than about 100 centipoise at 15° C. Heavy hydrocarbons may include aromatics or other complex ring hydrocarbons.

Heavy hydrocarbons may be found in a relatively permeable formation. The relatively permeable formation may include heavy hydrocarbons entrained in, for example, sand or carbonate. “Relatively permeable” is defined, with respect to formations or portions thereof, as an average permeability of 10 millidarcy or more (for example, 10 or 100 millidarcy). “Relatively low permeability” is defined, with respect to formations or portions thereof, as an average permeability of less than about 10 millidarcy. One darcy is equal to about 0.99 square micrometers. An impermeable layer generally has a permeability of less than about 0.1 millidarcy.

Certain types of formations that include heavy hydrocarbons may also include, but are not limited to, natural mineral waxes, or natural asphaltites. “Natural mineral waxes” typically occur in substantially tubular veins that may be several meters wide, several kilometers long, and hundreds of meters deep. “Natural asphaltites” include solid hydrocarbons of an aromatic composition and typically occur in large veins. In situ recovery of hydrocarbons from formations such as natural mineral waxes and natural asphaltites may include melting to form liquid hydrocarbons and/or solution mining of hydrocarbons from the formations.

“Hydrocarbons” are generally defined as molecules formed primarily by carbon and hydrogen atoms. Hydrocarbons may also include other elements such as, but not limited to, halogens, metallic elements, nitrogen, oxygen, and/or sulfur. Hydrocarbons may be, but are not limited to, kerogen, bitumen, pyrobitumen, oils, natural mineral waxes, and asphaltites. Hydrocarbons may be located in or adjacent to mineral matrices in the earth. Matrices may include, but are not limited to, sedimentary rock, sands, silicilytes, carbonates, diatomites, and other porous media. “Hydrocarbon fluids” are fluids that include hydrocarbons. Hydrocarbon fluids may include, entrain, or be entrained in non-hydrocarbon fluids such as hydrogen, nitrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, water, and ammonia.

An “in situ conversion process” refers to a process of heating a hydrocarbon containing formation from heat sources to raise the temperature of at least a portion of the formation above a pyrolysis temperature so that pyrolyzation fluid is produced in the formation.

An “in situ heat treatment process” refers to a process of heating a hydrocarbon containing formation with heat sources to raise the temperature of at least a portion of the formation above a temperature that results in mobilized fluid, visbreaking, and/or pyrolysis of hydrocarbon containing material so that mobilized fluids, visbroken fluids, and/or pyrolyzation fluids are produced in the formation.

“Insulated conductor” refers to any elongated material that is able to conduct electricity and that is covered, in whole or in part, by an electrically insulating material.

“Kerogen” is a solid, insoluble hydrocarbon that has been converted by natural degradation and that principally contains carbon, hydrogen, nitrogen, oxygen, and sulfur. Coal and oil shale are typical examples of materials that contain kerogen. “Bitumen” is a non-crystalline solid or viscous hydrocarbon material that is substantially soluble in carbon disulfide. “Oil” is a fluid containing a mixture of condensable hydrocarbons.

“Olefins” are molecules that include unsaturated hydrocarbons having one or more non-aromatic carbon-carbon double bonds.

“Orifices” refer to openings, such as openings in conduits, having a wide variety of sizes and cross-sectional shapes including, but not limited to, circles, ovals, squares, rectangles, triangles, slits, or other regular or irregular shapes.

“Perforations” include openings, slits, apertures, or holes in a wall of a conduit, tubular, pipe or other flow pathway that allow flow into or out of the conduit, tubular, pipe or other flow pathway.

“Pyrolysis” is the breaking of chemical bonds due to the application of heat. For example, pyrolysis may include transforming a compound into one or more other substances by heat alone. Heat may be transferred to a section of the formation to cause pyrolysis.

“Pyrolyzation fluids” or “pyrolysis products” refers to fluid produced substantially during pyrolysis of hydrocarbons. Fluid produced by pyrolysis reactions may mix with other fluids in a formation. The mixture would be considered pyrolyzation fluid or pyrolyzation product. As used herein, “pyrolysis zone” refers to a volume of a formation (for example, a relatively permeable formation such as a tar sands formation) that is reacted or reacting to form a pyrolyzation fluid.

“Rich layers” in a hydrocarbon containing formation are relatively thin layers (typically about 0.2 m to about 0.5 m thick). Rich layers generally have a richness of about 0.150 L/kg or greater. Some rich layers have a richness of about 0.170 L/kg or greater, of about 0.190 L/kg or greater, or of about 0.210 L/kg or greater. Lean layers of the formation have a richness of about 0.100 L/kg or less and are generally thicker than rich layers. The richness and locations of layers are determined, for example, by coring and subsequent Fischer assay of the core, density or neutron logging, or other logging methods. Rich layers may have a lower initial thermal conductivity than other layers of the formation. Typically, rich layers have a thermal conductivity 1.5 times to 3 times lower than the thermal conductivity of lean layers. In addition, rich layers have a higher thermal expansion coefficient than lean layers of the formation.

“Smart well technology” or “smart wellbore” refers to wells that incorporate downhole measurement and/or control. For injection wells, smart well technology may allow for controlled injection of fluid into the formation in desired zones. For production wells, smart well technology may allow for controlled production of formation fluid from selected zones. Some wells may include smart well technology that allows for formation fluid production from selected zones and simultaneous or staggered solution injection into other zones. Smart well technology may include fiber optic systems and control valves in the wellbore. A smart wellbore used for an in situ heat treatment process may be Westbay Multilevel Well System MP55 available from Westbay Instruments Inc. (Burnaby, British Columbia, Canada).

“Subsidence” is a downward movement of a portion of a formation relative to an initial elevation of the surface.

“Superposition of heat” refers to providing heat from two or more heat sources to a selected section of a formation such that the temperature of the formation at least at one location between the heat sources is influenced by the heat sources.

“Synthesis gas” is a mixture including hydrogen and carbon monoxide. Additional components of synthesis gas may include water, carbon dioxide, nitrogen, methane, and other gases. Synthesis gas may be generated by a variety of processes and feedstocks. Synthesis gas may be used for synthesizing a wide range of compounds.

“Tar” is a viscous hydrocarbon that generally has a viscosity greater than about 10,000 centipoise at 15° C. The specific gravity of tar generally is greater than 1.000. Tar may have an API gravity less than 10°.

A “tar sands formation” is a formation in which hydrocarbons are predominantly present in the form of heavy hydrocarbons and/or tar entrained in a mineral grain framework or other host lithology (for example, sand or carbonate). Examples of tar sands formations include formations such as the Athabasca formation, the Grosmont formation, and the Peace River formation, all three in Alberta, Canada; and the Faja formation in the Orinoco belt in Venezuela.

“Thermal fracture” refers to fractures created in a formation caused by expansion or contraction of a formation and/or fluids in the formation, which is in turn caused by increasing/decreasing the temperature of the formation and/or fluids in the formation, and/or by increasing/decreasing a pressure of fluids in the formation due to heating.

“Thickness” of a layer refers to the thickness of a cross section of the layer, wherein the cross section is normal to a face of the layer.

A “u-shaped wellbore” refers to a wellbore that extends from a first opening in the formation, through at least a portion of the formation, and out through a second opening in the formation. In this context, the wellbore may be only roughly in the shape of a “v” or “u”, with the understanding that the “legs” of the “u” do not need to be parallel to each other, or perpendicular to the “bottom” of the “u” for the wellbore to be considered “u-shaped”.

“Upgrade” refers to increasing the quality of hydrocarbons. For example, upgrading heavy hydrocarbons may result in an increase in the API gravity of the heavy hydrocarbons.

“Visbreaking” refers to the untangling of molecules in fluid during heat treatment and/or to the breaking of large molecules into smaller molecules during heat treatment, which results in a reduction of the viscosity of the fluid.

“Viscosity” refers to kinematic viscosity at 40° C. unless otherwise specified. Viscosity is as determined by ASTM Method D445.

The term “wellbore” refers to a hole in a formation made by drilling or insertion of a conduit into the formation. A wellbore may have a substantially circular cross section, or another cross-sectional shape. As used herein, the terms “well” and “opening,” when referring to an opening in the formation may be used interchangeably with the term “wellbore.”

Methods and systems for production and storage of hydrocarbons, hydrogen, carbon dioxide and/or other products from various subsurface formations such as hydrocarbon containing formations, or other desired formations that are used as an in situ storage sites.

A formation may be treated in various ways to produce many different products. Different stages or processes may be used to treat the formation during an in situ heat treatment process. In some embodiments, one or more sections of the formation are solution mined to remove soluble minerals from the sections. Solution mining minerals may be performed before, during, and/or after the in situ heat treatment process. In some embodiments, the average temperature of one or more sections being solution mined is maintained below about 120° C.

In some embodiments, one or more sections of the formation are heated to remove water from the sections and/or to remove methane and other volatile hydrocarbons from the sections. In some embodiments, the average temperature is raised from ambient temperature to temperatures below about 220° C. during removal of water and volatile hydrocarbons.

In some embodiments, one or more sections of the formation are heated to temperatures that allow for movement and/or visbreaking of hydrocarbons in the formation. In some embodiments, the average temperature of one or more sections of the formation are raised to mobilization temperatures of hydrocarbons in the sections (for example, to temperatures ranging from 100° C. to 250° C., from 120° C. to 240° C., or from 150° C. to 230° C.).

In some embodiments, one or more sections are heated to temperatures that allow for pyrolysis reactions in the formation. In some embodiments, the average temperature of one or more sections of the formation is raised to pyrolysis temperatures of hydrocarbons in the sections (for example, temperatures ranging from 230° C. to 900° C., from 240° C. to 400° C. or from 250° C. to 350° C.).

Heating the hydrocarbon containing formation with a plurality of heat sources may establish thermal gradients around the heat sources that raise the temperature of hydrocarbons in the formation to desired temperatures at desired heating rates. The rate of temperature increase through the mobilization temperature range and/or the pyrolysis temperature range for desired products may affect the quality and quantity of the formation fluids produced from the hydrocarbon containing formation. Slowly raising the temperature of the formation through the mobilization temperature range and/or pyrolysis temperature range may allow for the production of high quality, high API gravity hydrocarbons from the formation. Slowly raising the temperature of the formation through the mobilization temperature range and/or pyrolysis temperature range may allow for the removal of a large amount of the hydrocarbons present in the formation as hydrocarbon product.

In some in situ heat treatment embodiments, a portion of the formation is heated to a desired temperature instead of slowly raising the temperature through a temperature range. In some embodiments, the desired temperature is 300° C., 325° C., or 350° C. Other temperatures may be selected as the desired temperature.

Superposition of heat from heat sources allows the desired temperature to be relatively quickly and efficiently established in the formation. Energy input into the formation from the heat sources may be adjusted to maintain the temperature in the formation substantially at a desired temperature.

Mobilization and/or pyrolysis products may be produced from the formation through production wells. In some embodiments, the average temperature of one or more sections is raised to mobilization temperatures and hydrocarbons are produced from the production wells. The average temperature of one or more of the sections may be raised to pyrolysis temperatures after production due to mobilization decreases below a selected value. In some embodiments, the average temperature of one or more sections is raised to pyrolysis temperatures without significant production before reaching pyrolysis temperatures. Formation fluids including pyrolysis products may be produced through the production wells.

In some embodiments, the average temperature of one or more sections is raised to temperatures sufficient to allow synthesis gas production after mobilization and/or pyrolysis. In some embodiments, a temperature of hydrocarbons is raised to temperatures sufficient to allow synthesis gas production without significant production before reaching the temperatures sufficient to allow synthesis gas production. For example, synthesis gas may be produced in a temperature range from about 400° C. to about 1200° C., about 500° C. to about 1100° C., or about 550° C. to about 1000° C. A synthesis gas generating fluid (for example, steam and/or water) may be introduced into the sections to generate synthesis gas. Synthesis gas may be produced from production wells.

Solution mining, removal of volatile hydrocarbons and water, mobilizing hydrocarbons, pyrolyzing hydrocarbons, generating synthesis gas, and/or other processes may be performed during the in situ heat treatment process. In some embodiments, some processes are performed after the in situ heat treatment process. Such processes may include, but are not limited to, recovering heat from treated sections, storing fluids (for example, water and/or hydrocarbons) in previously treated sections, and/or sequestering carbon dioxide in previously treated sections.

FIG. 1 depicts a schematic view of an embodiment of a portion of the in situ heat treatment system for treating the hydrocarbon containing formation. The in situ heat treatment system may include barrier wells 100. Barrier wells are used to form a barrier around a treatment area. The barrier inhibits fluid flow into and/or out of the treatment area. Barrier wells include, but are not limited to, dewatering wells, vacuum wells, capture wells, injection wells, grout wells, freeze wells, or combinations thereof. In some embodiments, barrier wells 100 are dewatering wells. Dewatering wells may remove liquid water and/or inhibit liquid water from entering a portion of the formation to be heated, or to the formation being heated. In the embodiment depicted in FIG. 1, the barrier wells 100 are shown extending only along one side of heat sources 102, but the barrier wells typically encircle all heat sources 102 used, or to be used, to heat a treatment area of the formation.

In certain embodiments, a barrier may be formed in the formation after a solution mining process and/or an in situ heat treatment process by introducing a fluid into the formation. The barrier may inhibit formation fluid from entering the treatment area after the solution mining and/or the in situ heat treatment processes have ended. The barrier formed by introducing fluid into the formation may allow for isolation of the treatment area.

The fluid introduced into the formation to form the barrier may include wax, bitumen, heavy oil, sulfur, polymer, gel, saturated saline solution, and/or one or more reactants that react to form a precipitate, solid, or high viscosity fluid in the formation. In some embodiments, bitumen, heavy oil, reactants, and/or sulfur used to form the barrier are obtained from treatment facilities associated with the in situ heat treatment process. For example, sulfur may be obtained from a Claus process used to treat produced gases to remove hydrogen sulfide and other sulfur compounds.

The fluid may be introduced into the formation as a liquid, vapor, or mixed phase fluid. The fluid may be introduced into a portion of the formation that is at an elevated temperature. In some embodiments, the fluid is introduced into the formation through wells located near a perimeter of the treatment area. The fluid may be directed away from the interior of the treatment area. The elevated temperature of the formation maintains or allows the fluid to have a low viscosity such that the fluid moves away from the wells. At least a portion of the fluid may spread outwards in the formation towards a cooler portion of the formation. The relatively high permeability of the formation allows fluid introduced from one wellbore to spread and mix with fluid introduced from at least one other wellbore. In the cooler portion of the formation, the viscosity of the fluid increases, a portion of the fluid precipitates, and/or the fluid solidifies or thickens such that the fluid forms the barrier that inhibits flow of formation fluid into or out of the treatment area.

Heat sources 102 are placed in at least a portion of the formation. Heat sources 102 may include heaters such as insulated conductors, conductor-in-conduit heaters, surface burners, flameless distributed combustors, and/or natural distributed combustors. Heat sources 102 may also include other types of heaters. Heat sources 102 provide heat to at least a portion of the formation to heat hydrocarbons in the formation. Energy may be supplied to heat sources 102 through supply lines 104. Supply lines 104 may be structurally different depending on the type of heat source or heat sources used to heat the formation. Supply lines 104 for heat sources may transmit electricity for electric heaters, may transport fuel for combustors, or may transport heat exchange fluid that is circulated in the formation. In some embodiments, electricity for an in situ heat treatment process is provided by a nuclear power plant or nuclear power plants. The use of nuclear power may allow for reduction or elimination of carbon dioxide emissions from the in situ heat treatment process.

When the formation is heated, the heat input into the formation may cause expansion of the formation and geomechanical motion. The heat sources may be turned on before, at the same time, or during a dewatering process. Computer simulations may model formation response to heating. The computer simulations may be used to develop a pattern and time sequence for activating heat sources in the formation so that geomechanical motion of the formation does not adversely affect the functionality of heat sources, production wells, and other equipment in the formation.

Heating the formation may cause an increase in permeability and/or porosity of the formation. Increases in permeability and/or porosity may result from a reduction of mass in the formation due to vaporization and removal of water, removal of hydrocarbons, and/or creation of fractures from thermal stresses and/or the decomposition of nahcolite at high pressure. Fluid may flow more easily in the heated portion of the formation because of the increased permeability and/or porosity of the formation. Fluid in the heated portion of the formation may move a considerable distance through the formation because of the increased permeability and/or porosity. The considerable distance may be over 1000 m depending on various factors, such as permeability of the formation, properties of the fluid, temperature of the formation, and pressure gradient allowing movement of the fluid. The ability of fluid to travel considerable distance in the formation allows production wells 106 to be spaced relatively far apart in the formation.

Production wells 106 are used to remove formation fluid from the formation. In some embodiments, production well 106 includes a heat source. The heat source in the production well may heat one or more portions of the formation at or near the production well. In some in situ heat treatment process embodiments, the amount of heat supplied to the formation from the production well per meter of the production well is less than the amount of heat applied to the formation from a heat source that heats the formation per meter of the heat source. Heat applied to the formation from the production well may increase formation permeability adjacent to the production well by vaporizing and removing liquid phase fluid adjacent to the production well and/or by increasing the permeability of the formation adjacent to the production well by formation of macro and/or micro fractures.

More than one heat source may be positioned in the production well. A heat source in a lower portion of the production well may be turned off when superposition of heat from adjacent heat sources heats the formation sufficiently to counteract benefits provided by heating the formation with the production well. In some embodiments, the heat source in an upper portion of the production well remains on after the heat source in the lower portion of the production well is deactivated. The heat source in the upper portion of the well may inhibit condensation and reflux of formation fluid.

In some embodiments, the heat source in production well 106 allows for vapor phase removal of formation fluids from the formation. Providing heating at or through the production well may: (1) inhibit condensation and/or refluxing of production fluid when such production fluid is moving in the production well proximate the overburden, (2) increase heat input into the formation, (3) increase production rate from the production well as compared to a production well without a heat source, (4) inhibit condensation of high carbon number compounds (C₆ hydrocarbons and above) in the production well, and/or (5) increase formation permeability at or proximate the production well.

Subsurface pressure in the formation may correspond to the fluid pressure generated in the formation. As temperatures in the heated portion of the formation increase, the pressure in the heated portion may increase as a result of thermal expansion of in situ fluids, increased fluid generation and vaporization of water. Controlling a rate of fluid removal from the formation may allow for control of pressure in the formation. Pressure in the formation may be determined at a number of different locations, such as near or at production wells, near or at heat sources, or near or at monitor wells.

In some hydrocarbon containing formations, production of hydrocarbons from the formation is inhibited until at least some hydrocarbons in the formation have been mobilized and/or pyrolyzed. Formation fluid may be produced from the formation when the formation fluid is of a selected quality. In some embodiments, the selected quality includes an API gravity of at least about 20°, 30°, or 40°. Inhibiting production until at least some hydrocarbons are mobilized and/or pyrolyzed may increase conversion of heavy hydrocarbons to light hydrocarbons. Inhibiting initial production may minimize the production of heavy hydrocarbons from the formation. Production of substantial amounts of heavy hydrocarbons may require expensive equipment and/or reduce the life of production equipment.

In some hydrocarbon containing formations, hydrocarbons in the formation may be heated to mobilization and/or pyrolysis temperatures before substantial permeability has been generated in the heated portion of the formation. An initial lack of permeability may inhibit the transport of generated fluids to production wells 106. During initial heating, fluid pressure in the formation may increase proximate heat sources 102. The increased fluid pressure may be released, monitored, altered, and/or controlled through one or more heat sources 102. For example, selected heat sources 102 or separate pressure relief wells may include pressure relief valves that allow for removal of some fluid from the formation.

In some embodiments, pressure generated by expansion of mobilized fluids, pyrolysis fluids or other fluids generated in the formation is allowed to increase although an open path to production wells 106 or any other pressure sink may not yet exist in the formation. The fluid pressure may be allowed to increase towards a lithostatic pressure. Fractures in the hydrocarbon containing formation may form when the fluid approaches the lithostatic pressure due to thermal stresses and/or the decomposition of nahcolite at high pressures. For example, fractures may form from heat sources 102 to production wells 106 in the heated portion of the formation. The generation of fractures in the heated portion may relieve some of the pressure in the portion. Pressure in the formation may have to be maintained below a selected pressure to inhibit unwanted production, fracturing of the overburden or underburden, and/or coking of hydrocarbons in the formation.

After mobilization and/or pyrolysis temperatures are reached and production from the formation is allowed, pressure in the formation may be varied to alter and/or control a composition of formation fluid produced, to control a percentage of condensable fluid as compared to non-condensable fluid in the formation fluid, and/or to control an API gravity of formation fluid being produced. For example, decreasing pressure may result in production of a larger condensable fluid component. The condensable fluid component may contain a larger percentage of olefins.

In some in situ heat treatment process embodiments, pressure in the formation may be maintained high enough to promote production of formation fluid with an API gravity of greater than 20°. Maintaining increased pressure in the formation may inhibit formation subsidence during in situ heat treatment. Maintaining increased pressure may reduce or eliminate the need to compress formation fluids at the surface to transport the fluids in collection conduits to treatment facilities.

Maintaining increased pressure in a heated portion of the formation may surprisingly allow for production of large quantities of hydrocarbons of increased quality and of relatively low molecular weight. Pressure may be maintained so that formation fluid produced has a minimal amount of compounds above a selected carbon number. The selected carbon number may be at most 25, at most 20, at most 12, or at most 8. Some high carbon number compounds may be entrained in vapor in the formation and may be removed from the formation with the vapor. Maintaining increased pressure in the formation may inhibit entrainment of high carbon number compounds and/or multi-ring hydrocarbon compounds in the vapor. High carbon number compounds and/or multi-ring hydrocarbon compounds may remain in a liquid phase in the formation for significant time periods. The significant time periods may provide sufficient time for the compounds to pyrolyze to form lower carbon number compounds.

Generation of relatively low molecular weight hydrocarbons is believed to be due, in part, to autogenous generation and reaction of hydrogen in a portion of the hydrocarbon containing formation. For example, maintaining an increased pressure may force hydrogen generated during pyrolysis into the liquid phase within the formation. Heating the portion to a temperature in a pyrolysis temperature range may pyrolyze hydrocarbons in the formation to generate liquid phase pyrolyzation fluids. The generated liquid phase pyrolyzation fluids components may include double bonds and/or radicals. Hydrogen (H₂) in the liquid phase may reduce double bonds of the generated pyrolyzation fluids, thereby reducing a potential for polymerization or formation of long chain compounds from the generated pyrolyzation fluids. In addition, H₂ may also neutralize radicals in the generated pyrolyzation fluids. H₂ in the liquid phase may inhibit the generated pyrolyzation fluids from reacting with each other and/or with other compounds in the formation.

Formation fluid produced from production wells 106 may be transported through collection piping 108 to treatment facilities 110. Formation fluids may also be produced from heat sources 102. For example, fluid may be produced from heat sources 102 to control pressure in the formation adjacent to the heat sources. Fluid produced from heat sources 102 may be transported through tubing or piping to collection piping 108 or the produced fluid may be transported through tubing or piping directly to treatment facilities 110. Treatment facilities 110 may include separation units, reaction units, upgrading units, fuel cells, turbines, storage vessels, and/or other systems and units for processing produced formation fluids. The treatment facilities may form transportation fuel from at least a portion of the hydrocarbons produced from the formation. In some embodiments, the transportation fuel is jet fuel, such as JP-8.

Some hydrocarbon containing formations, such as oil shale formations, may include nahcolite, trona, halite, dawsonite, and/or other minerals within the formation. In some embodiments, nahcolite is contained in partially unleached or unleached portions of the formation. Unleached portions of the formation are parts of the formation where minerals have not been removed by groundwater in the formation. For example, in the Piceance basin in Colorado, U.S.A., unleached oil shale is found below a depth of about 500 m below grade. Deep unleached oil shale formations in the Piceance basin center tend to be relatively rich in hydrocarbons. For example, about 0.10 liters to about 0.15 liters of oil per kilogram (L/kg) of oil shale may be producible from an unleached oil shale formation.

Nahcolite is a mineral that includes sodium bicarbonate (NaHCO₃). Nahcolite may be found in the Parachute Creek member of the Green River Formation in Colorado and within the Green River Formation in Utah and Wyoming, U.S.A. In some embodiments, at least about 5 weight % nahcolite, at least about 10 weight % nahcolite, or at least about 20 weight % nahcolite are present in the formation. Dawsonite is a mineral that includes sodium aluminum carbonate (NaAl(CO₃) (OH)₂. Dawsonite is typically present in the formation at weight percents greater than about 2 weight % or, in some embodiments, greater than about 5 weight %. Nahcolite and/or dawsonite may dissociate at temperatures used in an in situ heat treatment process. The dissociation is strongly endothermic and may produce large amounts of carbon dioxide.

In some embodiments, nahcolite and/or dawsonite are solution mined prior to, during, and/or following treatment of the formation in situ to minimize dissociation reactions and/or to obtain desired chemical compounds or formation properties such as permeability. In certain embodiments, hot water or steam is used to dissolve nahcolite in situ to form an aqueous sodium bicarbonate solution before the in situ heat treatment process is used to process hydrocarbons in the formation. Nahcolite may form sodium ions (Na⁺) and bicarbonate ions (HCO3⁻) in aqueous solution. The solution may be produced from the formation through production wells, thus avoiding dissociation reactions during the in situ heat treatment process. In some embodiments, dawsonite is thermally decomposed to alumina during the in situ heat treatment process for treating hydrocarbons in the formation. The alumina is solution mined after completion of the in situ heat treatment process.

A perimeter barrier may be formed around the portion of the formation to be treated. The perimeter barrier may inhibit migration of water into the treatment area. During solution mining and/or the in situ heat treatment process, the perimeter barrier may inhibit migration of dissolved minerals and formation fluid from the treatment area. During initial heating, a portion of the formation to be treated may be raised to a temperature below the dissociation temperature of the nahcolite. The temperature may be at most about 90° C., or in some embodiments, at most about 80° C. The temperature may be any temperature that increases the solvation rate of nahcolite in water, but is also below a temperature at which nahcolite dissociates (above about 95° C. at atmospheric pressure).

A first fluid may be injected into the heated portion. The first fluid may include water, brine, steam, or other fluids that form a solution with nahcolite and/or dawsonite. The first fluid may be at an increased temperature, for example, about 90° C., about 95° C., or about 100° C. The increased temperature may be similar to the temperature of the portion of the formation.

In some embodiments, the first fluid is injected at an increased temperature into a portion of the formation that has not been heated by heat sources. The increased temperature may be a temperature below a boiling point of the first fluid, for example, about 90° C. for water. Providing the first fluid at an increased temperature increases a temperature of a portion of the formation. In certain embodiments, additional heat may be provided from one or more heat sources in the formation during and/or after injection of the first fluid.

In other embodiments, the first fluid is or includes steam. The steam may be produced by forming steam in a previously heated portion of the formation (for example, by passing water through u-shaped wellbores that have been used to heat the formation), by heat exchange with fluids produced from the formation, and/or by generating steam in standard steam production facilities. In some embodiments, the first fluid may be fluid introduced directly into a hot portion of the portion and produced from the hot portion of the formation. The first fluid may then be used as the first fluid for solution mining.

In some embodiments, heat from a hot previously treated portion of the formation is used to heat water, brine, and/or steam used for solution mining a new portion of the formation. Heat transfer fluid may be introduced into the hot previously treated portion of the formation. The heat transfer fluid may be water, steam, carbon dioxide, and/or other fluids. Heat may transfer from the hot formation to the heat transfer fluid. The heat transfer fluid is produced from the formation through production wells. The heat transfer fluid is sent to a heat exchanger. The heat exchanger may heat water, brine, and/or steam used as the first fluid to solution mine the new portion of the formation. The heat transfer fluid may be reintroduced into the heated portion of the formation to produce additional hot heat transfer fluid. In some embodiments, heat transfer fluid produced from the formation is treated to remove hydrocarbons or other materials before being reintroduced into the formation as part of a remediation process for the heated portion of the formation.

Steam injected for solution mining may have a temperature below the pyrolysis temperature of hydrocarbons in the formation. Injected steam may be at a temperature below 250° C., below 300° C., or below 400° C. The injected steam may be at a temperature of at least 150° C., at least 135° C., or at least 125° C. Injecting steam at pyrolysis temperatures may cause problems as hydrocarbons pyrolyze and hydrocarbon fines mix with the steam. The mixture of fines and steam may reduce permeability and/or cause plugging of production wells and the formation. Thus, the injected steam temperature is selected to inhibit plugging of the formation and/or wells in the formation.

The temperature of the first fluid may be varied during the solution mining process. As the solution mining progresses and the nahcolite being solution mined is farther away from the injection point, the first fluid temperature may be increased so that steam and/or water that reaches the nahcolite to be solution mined is at an elevated temperature below the dissociation temperature of the nahcolite. The steam and/or water that reaches the nahcolite is also at a temperature below a temperature that promotes plugging of the formation and/or wells in the formation (for example, the pyrolysis temperature of hydrocarbons in the formation).

A second fluid may be produced from the formation following injection of the first fluid into the formation. The second fluid may include material dissolved in the first fluid. For example, the second fluid may include carbonic acid or other hydrated carbonate compounds formed from the dissolution of nahcolite in the first fluid. The second fluid may also include minerals and/or metals. The minerals and/or metals may include sodium, aluminum, phosphorus, and other elements.

Solution mining the formation before the in situ heat treatment process allows initial heating of the formation to be provided by heat transfer from the first fluid used during solution mining. Solution mining nahcolite or other minerals that decompose or dissociate by means of endothermic reactions before the in situ heat treatment process avoids having energy supplied to heat the formation being used to support these endothermic reactions. Solution mining allows for production of minerals with commercial value. Removing nahcolite or other minerals before the in situ heat treatment process removes mass from the formation. Thus, less mass is present in the formation that needs to be heated to higher temperatures and heating the formation to higher temperatures may be achieved more quickly and/or more efficiently. Removing mass from the formation also may increase the permeability of the formation. Increasing the permeability may reduce the number of production wells needed for the in situ heat treatment process. In certain embodiments, solution mining before the in situ heat treatment process reduces the time delay between startup of heating of the formation and production of hydrocarbons by two years or more.

FIG. 2 depicts an embodiment of solution mining well 114. Solution mining well 114 may include insulated portion 116, input 118, packer 120, return 122, and casing 124. Insulated portion 116 may be adjacent to overburden 132 of the formation. In some embodiments, insulated portion 116 is low conductivity cement. The cement may be low density, low conductivity vermiculite cement or foam cement. Input 118 may direct the first fluid to treatment area 130. Perforations or other types of openings in input 118 allow the first fluid to contact formation material in treatment area 130. Packer 120 may be a bottom seal for input 118. First fluid passes through input 118 into the formation. First fluid dissolves minerals and becomes second fluid. The second fluid may be denser than the first fluid. An entrance into return 122 is typically located below the perforations or openings that allow the first fluid to enter the formation. Second fluid flows to return 122. The second fluid is removed from the formation through return 122. In some embodiments, more than one input 118 and/or more than one return 122 may be used in solution mining well 114.

FIG. 3 depicts an elevational view of an embodiment of wells used for solution mining and/or for an in situ heat treatment process. Solution mining wells 114 may be placed in the formation in an equilateral triangle pattern. In some embodiments, the spacing between solution mining wells 114 may be about 36 m. Other spacings may be used. The spacing between solution mining wells 114 may be, for example, between about 25 m and about 40 m. Heat sources 102 may also be placed in an equilateral triangle pattern. Solution mining wells 114 substitute for certain heat sources of the pattern. In the shown embodiment, the spacing between heat sources 102 is about 9 m. Other spacings may be used. The spacing between heat sources 102 may be, for example, between about 5 m and about 20 m. The ratio of solution mining well spacing to heat source spacing is 4. Other ratios may be used if desired. After solution mining is complete, solution mining wells 114 may be used as production wells for the in situ heat treatment process.

In some formations, a portion of the formation with unleached minerals may be below a leached portion of the formation. The unleached portion may be thick and substantially impermeable. A treatment area may be formed in the unleached portion. Unleached portion of the formation to the sides, above and/or below the treatment area may be used as barriers to fluid flow into and out of the treatment area. A first treatment area may be solution mined to remove minerals, increase permeability in the treatment area, and/or increase the richness of the hydrocarbons in the treatment area. After solution mining the first treatment area, in situ heat treatment may be used to treat a second treatment area. In some embodiments, the second treatment area is the same as the first treatment area. In some embodiments, the second treatment has a smaller volume than the first treatment area so that heat provided by outermost heat sources to the formation do not raise the temperature of unleached portions of the formation to the dissociation temperature of the minerals in the unleached portions.

In some embodiments, a leached or partially leached portion of the formation above or below an unleached portion of the formation may include significant amounts of hydrocarbon materials. An in situ heating process may be used to produce hydrocarbon fluids from the unleached portions and the leached or partially leached portions of the formation. FIG. 4 depicts a representation of a formation with unleached zone 126 below leached zone 128. Unleached zone 126 may have an initial permeability before solution mining of less than 0.1 millidarcy. Solution mining wells 114 may be placed in the formation. Solution mining wells 114 may include smart well technology that allows the position of first fluid entrance into the formation and second flow entrance into the solution mining wells to be changed. Solution mining wells 114 may be used to form first treatment area 130′ in unleached zone 126. Unleached zone 126 may initially be substantially impermeable. Unleached portions of the formation may form a top barrier and side barriers around first treatment area 130′. After solution mining first treatment area 130′, the portions of solution mining wells 114 adjacent to the first treatment area may be converted to production wells and/or heater wells.

Heat sources 102 in first treatment area 130′ may be used to heat the first treatment area to pyrolysis temperatures. In some embodiments, one or more heat sources 102 are placed in the formation before first treatment area 130′ is solution mined. The heat sources may be used to provide initial heating to the formation to raise the temperature of the formation and/or to test the functionality of the heat sources. In some embodiments, one or more heat sources are installed during solution mining of the first treatment area, or after solution mining is completed. After solution mining, heat sources 102 may be used to raise the temperature of at least a portion of first treatment area 130′ above the pyrolysis and/or mobilization temperature of hydrocarbons in the formation to result in the generation of mobile hydrocarbons in the first treatment area.

Barrier wells 100 may be introduced into the formation. Ends of barrier wells 100 may extend into and terminate in unleached zone 126. Unleached zone 126 may be impermeable. In some embodiments, barrier wells 100 are freeze wells. Barrier wells 100 may be used to form a barrier to fluid flow into or out of unleached zone 128. Barrier wells 100, overburden 132, and the unleached material above first treatment area 130′ may define second treatment area 130″. In some embodiments, a first fluid may be introduced into second treatment area 130″ through solution mining wells 114 to raise the initial temperature of the formation in second treatment area 130″ and remove any residual soluble minerals from the second treatment area. In some embodiments, the top barrier above first treatment area 130′ may be solution mined to remove minerals and combine first treatment area 130′ and second treatment area 130″ into one treatment area. After solution mining, heat sources may be activated to heat the treatment area to pyrolysis temperatures.

In certain embodiments, a section of a formation may be left untreated by solution mining and/or unleached. The unleached section may be proximate a selected section of the formation that has been leached and/or solution mined by providing the first fluid as described above. The unleached section may inhibit the flow of water into the selected section. In some embodiments, more than one unleached section may be proximate a selected section.

During in situ heat treatment of a nahcolite containing formation, the nahcolite in the formation may expand and/or decompose during heating of the formation. If there has not been sufficient connectivity (for example, permeability) and/or suitable accommodation space (for example, pore volume) created in the formation, the expanding/decomposing nahcolite may produce large forces that cause problems with heaters, production wells, and/or other mechanical structures in the subsurface during an in situ heat treatment process. To create connectivity and/or accommodation space in the formation, nahcolite may be solution mined prior to treatment of the formation using the in situ heat treatment process.

Solution mining of the entire treatment area, or a large portion (majority) of the treatment area, will typically create sufficient connectivity and suitable accommodation space for expansion/decomposition of nahcolite. Solution mining such large volumes of treatment area may, however, be time consuming and require extra infrastructure to produce products that are not necessarily cost effective to produce from the formation. In addition, solution mining too much nahcolite may oversupply the market for nahcolite products (for example, sodium carbonate).

Thus, in certain embodiments, a treatment area containing nahcolite is only partially solution mined before continuing with the in situ heat treatment process (for example, an in situ conversion process). Partial solution mining of the treatment area may include, for example, removing a selected minimum amount of nahcolite. The selected minimum amount of nahcolite removed may be the amount of nahcolite removed that creates the minimum connectivity and/or accommodation space needed in the treatment area to allow for expansion/decomposition of the remaining nahcolite during the in situ heat treatment process. For example, removing the selected minimum amount of nahcolite reduces forces produced by expansion/decomposition of the remaining nahcolite to acceptable levels (for example, levels that do not harm heaters, production wells, and/or other mechanical structures in the subsurface). Partial solution mining may remove sufficient amounts of nahcolite to accommodate expansion/decomposition during in situ heat treatment while reducing the time spent solution mining the formation, reducing surface infrastructure needed for treatment of solution mined nahcolite, and/or inhibiting sodium carbonate market saturation.

In certain embodiments, the treatment area (for example, hydrocarbon containing layer) is partially solution mined by solution mining one or more selected layers or intervals in the treatment area. For partial solution mining, layers may be selected for solution mining to remove a selected minimum amount of nahcolite (for example, the amount of nahcolite needed to be removed to create minimum connectivity and/or accommodation space in the treatment area to allow for expansion/decomposition of the remaining nahcolite during the in situ heat treatment process).

Layers in the formation may be differentiated by measurable transitions in the compositions and/or properties of the layers. For example, the layers may have noticeable transitions in the amount of nahcolite in the layers. In certain embodiments, the layers selected for solution mining contain higher percentages of nahcolite than other layers in the formation. In certain embodiments, layers that are selected for partial solution mining include, but are not limited to, layers that are at least about 30% by weight nahcolite, at least about 40% by weight nahcolite, at least about 50% by weight nahcolite, or at least about 60% by weight nahcolite (for example, layers with between about 40% and about 80% by weight nahcolite).

Factors for selection of layers for solution mining may also include other formation properties such as, but not limited to, hydrocarbon composition, permeability, and/or porosity. Other factors for selection of layers may include design parameters such as, but not limited to, number of layers to be solution mined, location of layers to be solution mined in the hydrocarbon containing layer, depth of layers, thickness of layers, proximity of layers to wells (for example, heaters wells or production wells) in the formation, spacing of solution mining wells. In addition, the number of layers, thickness of layers, location of layers and/or other design parameters may be selected based on the amount of connectivity needed in the hydrocarbon containing layer and/or the amount of accommodation space needed in the treatment area to allow for expansion/decomposition of nahcolite during the heating of the hydrocarbon containing layer.

In certain embodiments, the solution mined layers (intervals) selected are substantially horizontal or relatively horizontal layers in the treatment area as nahcolite composition tends to vary with depth in the formation (for example, nahcolite composition is relatively constant at a selected depth in the formation). In certain embodiments, layers selected for solution mining are relatively thin layers. For example, layers selected for solution mining may have thicknesses of at most about 6 m, about 3 m, or about 2 m (for example, layers selected may have a thickness of about 1.5 m). In comparison, the hydrocarbon containing layer in the treatment area may have a total thickness of about 100 m, about 150 m, or about 200 m. Thus, the total thickness of the solution mined layers may be a relatively small portion of the overall hydrocarbon containing layer thickness.

FIG. 5 depicts a cross-sectional representation of an embodiment of treatment area 130 being partially solution mined using selected layers of hydrocarbon containing layer 134. Hydrocarbon containing layer 134 includes layers 134A-F. In certain embodiments, layers 134B, 134D, and 134F have higher nahcolite weight percentage than layers 134A, 134C, and 134E. For example, layers 134B, 134D, and/or 134F may be at least about 40% by weight nahcolite while layers 134A, 134C, and 134E are less than about 40% by weight nahcolite. Layers 134B, 134D, and 134F may be at most about 2 m thick while layers 134A, 134C, and 134E have thicknesses of at least about 10 m.

In some embodiments, solution mining wells 114 are located in layers 134B and 134D. Solution mining wells may be horizontal (or substantially horizontal) solution mining wells. A first fluid such as water, heated water, and/or steam may be used to solution mine nahcolite from layers 134B and/or 134D and produce a second fluid (such as, but not limited to, sodium carbonate). In certain embodiments, layers 134B and 134D are solution mined using multiple solution mining wells 114 in each layer. FIG. 6 depicts a representation of an embodiment of a portion of treatment area 130 that is orthogonal to the treatment area depicted in FIG. 5 with solution mining wells 114 going in and out of the page in layers 134B and 134D.

In certain embodiments, solution mining wells 114 are used to solution mine a minimal amount of nahcolite from layers 134B and 134D. The minimal amount of nahcolite removed may be the amount of nahcolite needed to be removed to create minimum connectivity and/or accommodation space in treatment area 130 that allows for expansion/decomposition of the remaining nahcolite during subsequent in situ heat treatment of the treatment area. Thus, removing at least some nahcolite from layers 134B and 134D may be beneficial for further treatment of the formation using, for example, the in situ heat treatment process.

In some embodiments, the amount of nahcolite removed from layers 134B and/or 134D is at least about 0.5% by weight of the nahcolite in the layers and less than about 1% by weight of the nahcolite in the layers, less than about 2% by weight of the nahcolite in the layers, less than about 5% by weight of the nahcolite in the layers, less than about 10% by weight of the nahcolite in the layers, or less than about 20% by weight of the nahcolite in the layers. For example, the amount of nahcolite removed from layers 134B and/or 134D may be between about 0.5% by weight and about 20% by weight of the nahcolite in the layers or may be between about 0.5% by weight and about 5% by weight of the nahcolite in the layers. In some embodiments, the amount of nahcolite removed from layers 134B and/or 134D is between about 0.5% by weight of the nahcolite in the layers and about 50% by weight of the nahcolite in the layers, between about 5% by weight of the nahcolite in the layers and about 40% by weight of the nahcolite in the layers, or between about 15% by weight of the nahcolite in the layers and about 30% by weight of the nahcolite in the layers. In some embodiments, at most about 50%, at most about 30%, or at most about 20% by weight of the nahcolite in the layers is removed during solution mining of layers 134B and/or 134D. Removing nahcolite from layers 134B and/or 134D provides pore volume (accommodation space) for expansion in hydrocarbon containing layer 134 due to thermal expansion and/or decomposition of nahcolite or other materials during in situ heat treatment of treatment area 130.

After partial solution mining of layers 134B and/or 134D, treatment area 130 may be subjected to an in situ heat treatment process (for example, an in situ conversion process). Heaters may be used to provide heat to portions or all of treatment area 130 during the in situ heat treatment process. Production wells may be used to produce (remove) fluids from treatment area 130 during the in situ heat treatment process. The heaters and/or production wells along with other wells used during the in situ heat treatment process (for example, injection wells and/or monitoring wells) may be formed in treatment area 130 before, during, or after the partial solution mining process. The heaters and/or production wells may be located in any of layers 134A-F in hydrocarbon containing layer 134. In some embodiments, the heaters and/or production wells pass through multiple layers in hydrocarbon containing layer 134. In some embodiments, solution mining wells 114 in layers 134B and/or 134D are converted to heater wells, production wells, injection wells, and/or monitoring wells.

In some embodiments, fluids formed in treatment area 130 (such as mobilized and/or pyrolyzed hydrocarbons) move into layers 134B and/or 134D and are collected in the layers. For example, gases produced in treatment area 130 may be collected and produced in layer 134B. Liquids produced in the treatment area may be collected and produced in layer 134D. The gases and/or liquids may be produced through solution mining wells converted to production wells in layers 134B and/or 134D.

In some embodiments, following partial solution mining and in situ heat treatment of treatment area 130, the treatment area is used for storage (sequestration) of waste fluids. For example, carbon dioxide (CO₂), hydrogen sulfide (H₂S), and/or other acid gases may be stored in treatment area 130. After solution mining and in situ heat treatment, treatment area 130 may include one or more large heated volumes. In some embodiments, the heated volumes are separated by non-heated volumes maintained at lower temperatures and not treated. The heated volumes and non-heated volumes may be in an alternating pattern in the formation with heated volumes separated by non-heated volumes and vice versa. The non-heated volumes may provide support to the heated volumes during and after heat treatment.

The non-heated volumes may be smaller than the heated volumes. For example, the heated volumes may have volumes of at least about 2 times, at least about 3 times, or at least about 4 times the volumes of the non-heated volumes. In some embodiments, the heated and non-heated volumes have the same lengths and depths (heights) but have different widths that make the different size volumes. For example, the heated volumes may have widths of about 200 m while the non-heated volumes have widths of about 90 m.

In some embodiments, the heated volumes are cooled by providing (injecting) water into the heated volumes to quench the heated volume. The injected water may convert to steam because of the temperature in the heated volumes. Following cooling of the heated volumes, subsidence (compaction) of the formation is a potential problem because of unsupported void space in the heated volumes. In some embodiment, a fluid (for example, a liquid, compressible gas, or molten material) may be provided (injected) into the cooled, heated volumes to inhibit subsidence of the formation.

Typically, water may be provided into the cooled, heated volumes for abandonment/containment of the treatment area. Water, however, may have to be transported to the treatment area site for the sequestration and may be costly and wasteful to use for the abandonment/containment.

In some embodiments, materials produced during solution mining and/or in situ heat treatment of the treatment area are used for abandonment/containment of the treatment area. For example, carbon dioxide, hydrogen sulfide, or other acid gases may be sequestered in the treatment area to inhibit subsidence of the cooled, heated volumes in the treatment area. In some embodiments, other sulfur compounds are sequestered in the treatment area to inhibit subsidence of the cooled, heated volumes in the treatment area. Using such materials for the abandonment/containment of the treatment area may reduce costs by reducing the amount of waste materials that need to be treated or disposed and/or providing beneficial environmental considerations.

In some embodiments, the second fluid produced from the formation during solution mining is used to produce sodium bicarbonate. Sodium bicarbonate may be used in the food and pharmaceutical industries, in leather tanning, animal feed market, in fire retardation, in wastewater treatment, and in flue gas treatment (for example, flue gas desulfurization and hydrogen chloride reduction). The second fluid may be kept pressurized and at an elevated temperature when removed from the formation. The second fluid may be cooled in a crystallizer to precipitate sodium bicarbonate.

In some embodiments, the second fluid produced from the formation during solution mining is used to produce sodium carbonate, which may be referred to as soda ash. Sodium carbonate may be used in the manufacture of glass, in the manufacture of detergents, in water purification, polymer production, tanning, paper manufacturing, effluent neutralization, metal refining, sugar extraction, and/or cement manufacturing. The second fluid removed from the formation may be heated in a treatment facility to form sodium carbonate (soda ash) and/or sodium carbonate brine. Heating sodium bicarbonate will form sodium carbonate according to the equation:

2NaHCO₃→Na₂CO₃+CO₂+H₂O.  (EQN. 1)

In certain embodiments, the heat for heating the sodium bicarbonate is provided using heat from the formation. For example, a heat exchanger that uses steam produced from the water introduced into the hot formation may be used to heat the second fluid to dissociation temperatures of the sodium bicarbonate. In some embodiments, the second fluid is circulated through the formation to utilize heat in the formation for further reaction. Steam and/or hot water may also be added to facilitate circulation. The second fluid may be circulated through a heated portion of the formation that has been subjected to the in situ heat treatment process to produce hydrocarbons from the formation. At least a portion of the carbon dioxide generated during sodium carbonate dissociation may be adsorbed on carbon that remains in the formation after the in situ heat treatment process. In some embodiments, the second fluid is circulated through conduits previously used to heat the formation.

In some embodiments, higher temperatures are used in the formation (for example, above about 120° C., above about 130° C., above about 150° C., or below about 250° C.) during solution mining of nahcolite. The first fluid is introduced into the formation under pressure sufficient to inhibit sodium bicarbonate from dissociating to produce carbon dioxide. The pressure in the formation may be maintained at sufficiently high pressures to inhibit such nahcolite dissociation but below pressures that would result in fracturing the formation. In addition, the pressure in the formation may be maintained high enough to inhibit steam formation if hot water is being introduced in the formation. In some embodiments, a portion of the nahcolite may begin to decompose in situ. In such cases, the sodium is removed from the formation as soda ash. If soda ash is produced from solution mining of nahcolite, the soda ash may be transported to a separate facility for treatment. The soda ash may be transported through a pipeline to the separate facility.

As described above, in certain embodiments, following removal of nahcolite from the formation, the formation is treated using the in situ heat treatment process to produce formation fluids from the formation. In some embodiments, the formation is treated using the in situ heat treatment process before solution mining nahcolite from the formation. The nahcolite may be converted to sodium carbonate (from sodium bicarbonate) during the in situ heat treatment process. The sodium carbonate may be solution mined as described above for solution mining nahcolite prior to the in situ heat treatment process.

Using an in situ heat treatment process to treat formations with minerals (such as nahcolitic oil shale formations) presents certain problems. For example, minerals in the formation may expand and/or decompose during heating of the formation and/or there may be uncertainty with how much and where the minerals are located. Uncertainty in the location and/or the amount of minerals in the formation may make it difficult to efficiently and/or affordably leach or remove the minerals from the formation. For example, if the nahcolite is located in nodules, water may leach only the nodule the water is injected into without touching any nodules nearby if there is no connectivity between the nodules. Without removing the minerals from the formation, heating of the formation may be unpredictable and/or require large energy expenditures if the minerals react endothermically during heat treatment of the formation. Additionally, management of some minerals (for example, nahcolite) may be difficult and/or costly. For example, solution mining too much nahcolite may oversupply the market for nahcolite products such as sodium carbonate.

As described above, solution mining of the entire treatment area, or a portion of the treatment area, may create sufficient connectivity and suitable accommodation space for expansion/decomposition of nahcolite. Solution mining, however, may be undesirable (for example, because of unpredictability of the location and/or amount of minerals). Without solution mining, however, there may not be sufficient connectivity (permeability) and/or suitable accommodation space (pore volume) in the formation for heat treatment of the formation.

To overcome issues with heat treatment of the formation without solution mining the formation, connectivity and/or accommodation space may be created in a treatment area containing minerals (for example, nahcolite) by fracturing, or partial fracturing, of the treatment area prior to heating the formation. Fracturing the formation may create permeaiblity and/or pore volume in or near wellbores used to produce the fractures to provide sufficient connectivity and/or accommodation space for heat treatment of the formation.

Typical nahcolitic oil shale formations have horizontal permeability that is significantly higher than vertical permeability (for example, horizontal permeability is ten (10) times greater than vertical permeability). Thus, in certain embodiments, nahcolitc oil shale formations are treated using vertical production wells. FIG. 7A depicts a side-view representation of an embodiment for treating a formation using an in situ heat treatment process with vertical production wells. FIG. 7B depicts an end-view representation of the embodiment shown in FIG. 7A. FIG. 7C depicts a top-view representation of the embodiment shown FIG. 7A. Treatment area 130 may be located at a depth below the surface of a hydrocarbon containing formation. For example, treatment area 130 may be located below an overburden of the formation. In some embodiments, the overburden has depths of between about 1000 feet (about 300 m) and about 5000 feet (about 1500 m)(for example, about 2000 feet (about 600 m)). In some embodiments, treatment area 130 is located below a layer (or crown) of nahcolite and/or other minerals. The nahcolite layer may be used as a barrier for treatment area 130 (for example, a barrier with a minimum thickness between the treatment area and an aquifer).

In certain embodiments, production wells 106 are located substantially vertically in treatment area 130. Heaters 136 are located substantially horizontally in treatment area 130. Heaters 136 may be arranged in a semi-irregular pattern due to the varied permeability and/or distribution of components in treatment area 130. For example, heaters 136 may have tighter spacing at or near the edges of treatment area 130, as shown in FIG. 7A.

In certain embodiments, vertical production wells 106 are used in treatment area 130 due to the higher horizontal permeability in the treatment area. Typical reservoir models (for example, STARS simulations) show that vertical production wells will provide better recovery of products for a formation with higher horizontal permeability. A problem with using vertical production wells in oil shale formations is that a large number of production wells is needed to access the formation, as shown in FIG. 7C. The large number of production wells is typically needed to access a greater volume of the formation, and provide higher product recovery, because of the limited connectivity between production wells in the formation.

To reduce the number of production wells needed for the in situ heat treatment process, horizontal (for example, substantially horizontal) production wells may be used. Using horizontal production wells, however, may not be feasible in formations with low vertical permeability because the limited vertical connectivity inhibits recovery of products from areas above and below the production wells in the formation.

To overcome the problems with connectivity in using horizontal production wells, in certain embodiments, fractures initiated from horizontal production wells are used to create permeability in the formation. FIG. 8A depicts a side-view representation of an embodiment for treating a formation using an in situ heat treatment process with horizontal production wells and fractures initiated in the production wells. FIG. 8B depicts an end-view representation of the embodiment shown in FIG. 8A. FIG. 8C depicts a top-view representation of the embodiment shown FIG. 8A. Heaters 136 and production wells 106 may be substantially horizontal in treatment area 130. In certain embodiments, as shown in FIGS. 8A and 8B, heaters 136 and production wells 106 are substantially parallel in treatment area 130. In certain embodiments, production wells 106 replace one or more heaters 136 near a center of treatment area 130, as shown in FIG. 8A.

FIG. 9A depicts a side-view representation of another embodiment for treating a formation using an in situ heat treatment process with horizontal production wells and fractures initiated in the production wells. FIG. 9B depicts an end-view representation of the embodiment shown in FIG. 9A. In certain embodiments, as shown in FIGS. 9A and 9B, heaters 136 and production well 106 are substantially perpendicular in treatment area 130. Production well 106 may be located at a depth that is vertically between depths of heaters 136 such that the production well does not intersect with any of the heaters.

As shown in FIGS. 8A and 8B and FIGS. 9A and 9B, fractures 138 may be formed from production wells 106. In certain embodiments, fractures 138 are formed substantially vertically in treatment area 130. Providing substantially vertical fractures 138 increases the vertical permeability in treatment area 130. Increasing the vertical permeability increases the average reservoir permeability in treatment area 130. Because of the increase in average reservoir permeability, fewer production wells 106 may be needed for in situ heat treatment of treatment area 130. For example, up to 10× fewer production wells 106 may be needed with substantially vertical fractures 138 formed at selected intervals along the production wells as compared to using substantially vertical production wells (as shown in FIGS. 7A-C). Reducing the number of wells formed in the formation may reduce costs associated with forming and/or maintaining the wells. In addition, using horizontal production wells may reduce a surface footprint for treating the formation with the in situ heat treatment process.

In certain embodiments, oil recovery during in situ heat treatment of treatment area 130 is increased due to the increased average reservoir permeability with fractures 138. Fractures 138 may also reduce the pore pressure at or near production wells 106 by reducing the back pressure at the production wells. Reducing the pore pressure may increase the production of liquid hydrocarbons versus production of gas and/or coke. Thus, having fractures 138 in treatment area 130 may potentially improve the economic performance of the in situ heat treatment process.

Fractures 138 may be formed using techniques known in the art for forming fractures in hydrocarbon containing formations such as oil shale formations. Examples of fracturing techniques include hydraulic fracturing, acid fracturing, pneumatic fracturing and combinations thereof. In some embodiments, fractures 138 are formed using a multi-stage fracturing system. The multi-stage fracturing system may form fractures at selected intervals along a well (for example, production well 106) by fracturing at a first location along the well, inhibiting further fracturing at the first location (for example, plugging the well at the first location), and then forming another fracture at a second location at a selected interval from the first location along the well. The fracturing/plugging process may be repeated at multiple intervals along the length of the well to provide fractures at the selected intervals along the length of the well. Seismic and/or microseismic technology may be used to assess the size and/or shape of fractures formed in the formation. FIG. 8B depicts two fractures 138 formed at selected intervals along a portion of production well 106. FIG. 9A depicts five fractures 138 formed at selected intervals along a portion of production well 106. The interval between fractures 138 may be selected based on factors including, but not limited to, properties of treatment area 130, size of treatment area 130, orientation of production well 106, located of production well 106, and desired production from treatment area 130.

As an example, fractures 138 may be formed at intervals of about 200 feet (about 60 m) for a 3500 feet (about 1066 m) long production well 106 with the production well parallel to heaters 136, as shown in FIG. 8B. As another example, fractures 138 may be formed at intervals of about 150 feet (about 45 m) for a 3400 feet (about 1036 m) long production well 106 with the production well perpendicular to heaters 136, as shown in FIG. 9A. The number and/or spacing of fractures 138 may be optimized to, for example, provide the best economic recovery of hydrocarbons from treatment area 130. For example, the number and/or spacing of fractures 138 may be optimized using a simulation such as a STARS simulation.

In some embodiments, fractures 138 are kept open (inhibit from closing during in situ heat treatment) using one or more proppants provided into the fractures. In some embodiments, fractures 138 formed from adjacent production wells 106 that are substantially parallel to heaters 136 are offset to inhibit overlapping of the fractures, as shown in FIG. 8C. In some embodiments, heaters 136 are placed (for example, wellbores drilled and/or heaters installed) in treatment area 130 after formation of fractures 138. Placing heaters 136 in the formation after forming fractures 138 may inhibit damage the heaters caused by the fracturing process.

In certain embodiments, fractures 138 have an upward bias due to formation conditions. For example, the formation may have less stress in upper portions of the formation than bottom portions of the formation. Thus, in certain embodiments, production wells 106 are positioned with a bias towards the bottom of treatment area 130, as shown in FIGS. 8A, 8B, 9A, and 9B. In certain embodiments, fractures 138 tend to be slowed and/or stopped by interfaces between rocks in the formation. Thus, fractures 138 may have an oblong cross-section, as shown in FIGS. 9A and 9B.

In certain embodiments, fluid is injected through one or more fractures 138 formed in the formation. In some embodiments, the fluid is injected before heating the formation and/or before placing heaters in the formation. FIG. 10A depicts a side-view representation of an embodiment for treating a formation with fluid injection through fractures initiated in production wells. FIG. 10B depicts an end-view representation of the embodiment shown in FIG. 10A. Fractures 138 may be formed from production well 106 similarly to the embodiment depicted in FIGS. 9A and 9B. In some embodiments, production well 106 is moved closer to the bottom of treatment area 130 for the injection embodiment, as shown in FIGS. 10A and 10B.

As shown in FIGS. 10A and 10B, injection well 140 is located at or near the top of fractures 138. Injection well 140 may be used for injection of fluid into fractures 138. Injection of fluid may form injection zones 142 around fractures 138. The injected fluid may flow through injection zones 142 and into production well 106. Production well 106 may be used to remove fluid from injection zones 142 that is cooler than fluid injected from injection well 140.

In certain embodiments, hot water and/or steam is injected into fractures 138. Hot water and/or steam may be generated from, for example, other treatment areas (for example, previously treated formations), hot production fluids, and/or power plant waste heat. In some embodiments, hot water and/or steam are generated using a gas furnace (for example, burning of produced hydrocarbons) or solar heating. Using hot water and/or steam generated from such sources may reduce costs associated with heating treatment area 130.

In certain embodiments, heated injection fluid provides some heat to treatment area 130 in and around injection zones 142. For example, heated injection fluid may preheat portions of treatment area 130 for heating with heaters 136. Preheating treatment area 130 with the heated injection fluid may increase the average heating efficiency for in situ heat treatment of the treatment area. For example, preheating treatment area 130 with the heated injection fluid may reduce the heating or power requirement for heaters 136. In some embodiments, preheating treatment area 130 with the heated injection fluid allows one or more heaters 136 to be removed from the pattern of heaters. For example, heaters may not be needed in or near injection zones 142, as shown in FIG. 10A.

In some embodiments, injection of heated injection fluid such as hot water and/or steam leaches (removes) minerals such as nahcolite from in or around injection zones 142. Leached minerals may be removed through production well 106. Thus, injection of hot water and/or steam may provide at least some solution mining of treatment area 130. Solution mining of treatment area 130 may reduce the overall mass to be heated inside the treatment area, increase the permeability of the treatment area, and/or provide economic benefits associated with production and/or recovery of nahcolite from the treatment area.

In some embodiments, one or more fractures 138 are formed from heater wells (for example, heaters 136). For example, fractures 138 may be formed from both heaters 136 and production wells 106 in the embodiment depicted in FIG. 9A. Forming fractures 138 from both heaters 136 and production wells 106 may produce at least some fractures that are perpendicular (orthogonal) to each other. Forming orthogonal fractures may further increase the average reservoir permeability in the treatment area.

In some embodiments, treatment area 130 with fractures 138 is located adjacent to another treatment area in the formation that does not have fractures. In some embodiments, multiple treatment areas with fractures may be interspersed with treatment areas that do not have fractures. For example, the differing treatment areas may form a checkerboard pattern of treatment areas with fractures and treatment areas without fractures. In some embodiments, wells may be formed in treatment areas without fractures to produce fluids from the formation and/or inject fluids into the formation. For example, a well in a treatment area without fractures may be used to produce cooler fluids generated in an adjacent treatment area with fractures. Producing fluids from the adjacent treatment area may be possible because of the horizontal permeability of the untreated formation.

In some embodiments, formations other than oil shale formations with nahcolite are treated using the embodiments of fractures 138 described herein and/or variants on the embodiments of the fractures described herein. For example, tar sand formations such as carbonate formations (for example, the Grosmont formation in Alberta, Canada) may be treated using the embodiments of fractures 138 described herein. In some embodiments, horizontal fractures may be advantageously used in treating certain formations (for example, formations with higher vertical permeability than horizontal permeability).

It is to be understood the invention is not limited to particular systems described which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification, the singular forms “a”, “an” and “the” include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to “a layer” includes a combination of two or more layers and reference to “a fluid” includes mixtures of fluids.

In this patent, certain U.S. patents and U.S. patent applications have been incorporated by reference. The text of such U.S. patents and U.S. patent applications is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference U.S. patents and U.S. patent applications is specifically not incorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 

What is claimed is:
 1. A method for treating a hydrocarbon containing layer in a subsurface formation, comprising: forming a plurality of substantially vertical fractures in the formation at selected intervals along a length of at least one production wellbore positioned substantially horizontally in the hydrocarbon containing layer; providing heat from a plurality of heaters to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized, wherein at least some of the plurality of heaters are positioned substantially horizontally in the hydrocarbon containing layer; and producing at least some mobilized hydrocarbons through at least one production wellbore.
 2. The method of claim 1, further comprising forming the fractures at substantially equidistant intervals along the length of the production wellbore.
 3. The method of claim 1, wherein the heaters are positioned in heater wellbores.
 4. The method of claim 1, wherein the heaters are positioned substantially parallel with the at least one production wellbore.
 5. The method of claim 1, wherein the heaters are positioned substantially perpendicular to the at least one production wellbore.
 6. The method of claim 1, wherein the fractures have oblong cross-sections.
 7. The method of claim 1, wherein the at least one production wellbore is located closer to a bottom of the hydrocarbon containing layer than a top of the hydrocarbon containing layer.
 8. The method of claim 1, further comprising providing a proppant to keep one or more of the fractures open.
 9. The method of claim 1, further comprising providing heated injection fluid into at least one of the fractures.
 10. The method of claim 1, further comprising providing heated injection fluid into at least one of the fractures to provide at least some heat to the hydrocarbon containing layer.
 11. A method for treating a hydrocarbon containing layer in a subsurface formation, comprising: forming a plurality of substantially vertical fractures in the formation at selected intervals along lengths of a plurality of production wellbores positioned substantially horizontally in the hydrocarbon containing layer; providing heat from a plurality of heaters to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized, wherein at least some of the plurality of heaters are positioned substantially horizontally in the hydrocarbon containing layer; and producing at least some mobilized hydrocarbons through at least one of the production wellbores.
 12. The method of claim 11, further comprising forming the fractures at substantially equidistant intervals along the length of at least one of the production wellbores.
 13. The method of claim 11, wherein at least a portion of one of the fractures formed along at least one of the production wellbores overlaps with a portion of at least one of the fractures formed along an adjacent production wellbore.
 14. The method of claim 11, wherein the heaters are positioned in heater wellbores.
 15. The method of claim 11, wherein the heaters are positioned substantially parallel with the production wellbores.
 16. The method of claim 11, wherein the heaters are positioned substantially perpendicular to the production wellbores.
 17. The method of claim 11, wherein the fractures have oblong cross-sections.
 18. The method of claim 11, wherein at least one of the production wellbores is located closer to a bottom of the hydrocarbon containing layer than a top of the hydrocarbon containing layer.
 19. The method of claim 11, further comprising providing a proppant to keep one or more of the fractures open.
 20. The method of claim 11, further comprising providing heated injection fluid into at least one of the fractures.
 21. The method of claim 11, further comprising providing heated injection fluid into at least one of the fractures to provide at least some heat to the hydrocarbon containing layer.
 22. A system configured for treating a hydrocarbon containing layer in a subsurface formation, comprising: a plurality of production wellbores positioned substantially horizontally in the hydrocarbon containing layer; a plurality of heaters positioned substantially horizontally in the hydrocarbon containing layer, wherein the heaters are configured to provide heat to the hydrocarbon containing layer such that at least some hydrocarbons in the hydrocarbon containing layer are mobilized during use; and a plurality of substantially vertical fractures formed in the formation at selected intervals along a length of at least one of the production wellbores.
 23. The system of claim 22, wherein the heaters are positioned in heater wellbores.
 24. The system of claim 22, wherein the heaters are positioned substantially parallel with the production wellbores.
 25. The system of claim 22, wherein the heaters are positioned substantially perpendicular to the production wellbores.
 26. The system of claim 22, wherein the fractures have oblong cross-sections.
 27. The system of claim 22, wherein at least one of the production wellbores is located closer to a bottom of the hydrocarbon containing layer than a top of the hydrocarbon containing layer. 